(a) Technical Field
The present invention relates to an antifouling coating composition comprising a novel perfluoropolyether-modified silane compound in order to improve antifouling property, scratch resistance and durability, and a film formed by coating the composition.
(b) Background Art
Fluorine-based functional materials are drawing attention worldwide as a core material in the next-generation technology, including optical communications, optoelectronics, semiconductors, automobiles and computer industries. The demand on optical films used in various displays including liquid crystal displays (LCDs) is on the rapid increase. An optical film comprises a liquid crystal or polarizing layer, a hard coat layer to protect the liquid crystal and provide flatness, an antireflection layer to prevent optical interference and provide clear images, and an antifouling layer to prevent surface contamination. Especially, the techniques for fabricating optical films having an antifouling layer are very important from the industrial point of view.
At present, antireflection film is formed of multi-layers of thin inorganic oxide films with very high hydrophilicity for refractive index and thickness control. Thus, it is contaminated easily during use, and the contaminant is not removed easily. In case a solvent is used to remove the contaminant, there is a risk of damaging the surface of the film. In order to provide antifouling property and water repellency to the surface of an optical functional film, glass, etc., a silicone or fluorocarbon polymer is used on the outermost surface to form a cured film.
Examples of the materials used for coating the surface include C8F17C2H4Si(NH)3/2, C4F9C2H4Si(NH)3/2 and polysiloxazane [U.S. Pat. No. 4,678,688]. When these compounds are used alone, abrasion durability is deteriorated because of insufficient crosslinking with the inorganic oxide substrate. When only the fluorocarbon is used, satisfactory antifouling property is not attained. When the polysiloxazane compound is used, initial antifouling property is deteriorated because the polysiloxazane has a relatively larger surface energy than the fluorocarbon. Further, sufficient crosslinking may not be attained due to the insufficiency of the functional groups required to form a three-dimensional structure. As a result, contaminants may accumulate or adhere and fingerprints may remain due to low glass transition temperature. In Japanese Patent Publication No. 1990-233535, a silane compound having perfluoro groups is used as a glass surface modifier, but the resultant coating does not exhibit sufficient water repellency, antifouling property and/or nonfouling property.
In order to solve this problem, the so-called silane coupling technique of combining an inorganic material such as glass with an organic material has been proposed. A silane coupling agent has an organic functional radical or a chemical structure with good affinity with an organic material and a reactive alkoxysilyl radical in a molecule. The alkoxysilyl radical undergoes self-condensation reaction with air-borne moisture, converting to a siloxane to form a coating. At the same time, the silane coupling agent forms chemical and physical bonds with the surface of glass or metal, resulting in a durable tough coating. By virtue of these advantages, the silane coupling agent is widely used as a coating agent or a primer to a variety of substrates.
The compounds obtained by introducing perfluoro groups to the silane coupling agent through chemical bonding are disclosed as coating agents with good film formability, adhesivity to substrates and durability [Japanese Patent Laid-open No. Sho 58-167597, Japanese Patent Laid-open Nos. Sho 58-122979, Hei 10-232301 and Hei 2000-143991]. According to the patents, it is mentioned that the introduction of perfluoroalkyl groups on the surface of a substrate having a silane coupling structure improves antifouling properties (water and oil repellency). These compounds, however, fail to have enough oil repellency because the length (molecular weight) of the perfluoro radical portion is restricted, or, in case the perfluoro radical portion is sufficiently long, the proportion taken up by the alkoxysilyl radical in the whole molecule including the perfluoro groups decreases, thereby resulting in poor adhesivity or adhesion durability.
The above information in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.